Transmitting tube



June 15, 1948. A. GAUDENZH ET AL 2,443,237

. TRANSMITTING TUBE Filed March 21, 1944 I 2 Sheets-Sheet 1 June 15, 948. A. GAUDENZI ET AL 2,443,237

TRANSMITTING TUBE Filed March 21, 1944 T 2 Sheets-Sheet 2 atenteol .i'une 15, 1948 TRANSMITTING TUBE Arthur Gaudenzi, Wettingen, and Otto Schtirli, Baden, Switzerland, assignors to Patelhold Patentverwertungs- & Elektro-Holding A.-G., Glarus, Switzerland, a corporation Application March 21, 1944, Serial No. 527,500 In Switzerland May 23, 1941 13 Claims. 1

This invention relates to transmitting tubes and more particularly to tubes of the demountable type in which the tube enveloped is formed of a number of wall sections that are bolted or otherwise held in assembled relation. At least one of the joints between wall sections is sealed by plastic material and the envelope is exhausted, during operation of the tube, by a vacuum pump that runs either continuously or intermittently, depending upon the regulating system, to establish and maintain the required degree of vacuum within the tube.

In high-vacuum tubes electrons from the emitting cathode only reach the control grid when the potential of this grid is higher thanthat of the cathode. When these so-called primary electrons reach the grid, secondary electrons are released from the surface of the grid which generally travel on to the anode. A current will thus flow in the grid circuit which corresponds to the difierence between the primary electron current ending at the grid and the secondary electron current commencing at the grid. This is based on a the assumption, which is generally correct, that the discharge path is free from moving ions which would in their effect superimpose themselves on the aforementioned electron currents.

The number of secondary electrons Which can be released by a primary electron depends only very slightly on the grid material and practically not at all on its temperature. The yield is, however, in the first place dependent on the grid voltage Ug, that is on the difierencein potential between the grid and the cathode and also on the angle of impact of the primary electrons causing the secondary emission. Up to a voltage of 500 volts, with an impact perpendicular to the surface of the grid, the yield increases rapidly and then decreases slowly and continuously as the voltage exceeds this value. When the inclination of the electron path towards the vertical direction of impact increases, the yield of secondary electrons also increases, and the reversal in the rate of secondary emission occurs at a higher value of grid voltage. The secondary current thus varies with the grid voltage and it is also considerably influenced by the value of the anode voltage and the relative locatiion of the electrodes. When the secondary electron current exceeds the primary electron current, the direction of the current in the grid circuit is reversed.

Such an irregular relationship between the grid current and grid voltage, which furthermore changes during service as experience has shown,

results in a large variation in the loading of the control stage connected to the grid. When transmitting tubes are used whose characteristic curves have negative portions, wild oscillations can easily occur which together with the varying load on the control stage may cause appreciable distortions in the transmission. Although with transmitters which are employed only for the generation of high frequency power, for instance for chemical or thermal purposes, a high distortion factor is of minor consideration, even in such cases a grid current which increases rapidly with the grid voltage may be a disadvantage because the control stage may under certain conditions not be in a position to supply the corresponding grid power. Sealed-off transmitting tubes according to their constructional form and power have characteristics which are different for each particular tube. Such tubes must therefore be carefully selected for the purpose for which they are intended and this requires that large stocks have to be maintained and each tube tried out until the 7 most suitable one is found.

A great advantage would, however, be achieved if the course or shape of the grid current curve could subsequently be adjusted to suit the problem under consideration. By this means the replacement of such tubes would be greatly simplified and spare stocks could be kept consider-- ably smaller. Tubes which have for instance to operate in push-pull connection could then also be adjusted as regards the grid currents so that distortion is still further reduced. Above all, however, the best possible grid current curve for each constructional form of tube, could be obtained independently of the various differences due to manufacture. In the ideal case for instance the grid current should only increase slightly with the grid voltage and then remain appoximately constant at higher voltages.

Objects of this invention are to provide electron tubes havin'gparts that are relatively movable, during operation of the tubes, to attain the advantage above stated. An object is to provide a demountable'tube having cathode and control grid elements arranged and supported for angular adjustment to alter the grid current characteristic of the tube. More specifically, an object is to provide a demountable tube having a cathode in the form of parallel hot wires parallel to the tube axis, a control grid consisting of or including a plurality of rods parallel to the cathode wires, and supporting members for the oathode and grid electrodes that are angularly adjustable about the tube axis in such a manner that these electrodes can be rotated relatively to each other even when the tube is in operation.

Figs. 1 and 2 are grid voltage-grid current curve sheets typical of two tubes that exhibit, respectively, an irregular and a regular relationship. of current and volta e;

Figs. 3a and 3b are schematic cross-sections through the cathode and control grid electrodes of a tube embodying the invention, the views.

showing different angular relationships of the electrodes;

Figs. 4a and 4b are similar schematic cross-'sections showing different relative locations of the electrodes in another embodiment of the invention;

Fig. 5 shows a constructional example of a demountable tube in longitudinal section, whilst Figs. 6-8 are cross-sectional views to an enlarged scale of thistube, along the lines of sections 6-6, l? and 88 of Fig. 5, respectively.

In the Figs. 1 and 2 curve sheets, the abscissae represent the grid voltage Ug and the ordinates represent values of grid current and grid current components established during operation of two tubes of different electrode geometry. The resultant grid current Jg, which is the dominant value, can be measured and plotted against impressed values of grid voltage Ug. The grid current may be assumed to be the difference [between the primary electron current J 10 causing the secondary emission and the secondary electron current Js. If thelatter predominateathe resultant grid current Jg will become negative and there will bea sharp drop in the grid currentgrid voltage characteristic curve, for example over the range of from 200 to 500 volts on the grid in the case illustratedby theFig. 1 curve. When the primary electron current Jp is greater than the corresponding values of secondary electron current Js over theentire grid voltage range, the resultant grid current Jg doesnot fall, to negative values, see Fig. 2. Electrode arrangements that result indiiferent grid current characteristics arepshown schematically, Figs.,l3a to 4b,, in cross-section through the cathode-and control gridperpendicular to the tube aXis.. The wires of the cathodeK and, the rodsG of the grid,.which in this case is assumed tobe arod grid, can according to Figs. 3a. and 3b be located in two symmetrical positionswhich are obtained by a relative rotation ofA57. Between these extreme. positions a uniform variationof the relative positions of. these electrodes is. possible. The anode is. to be considered as a coaxial cylinder which surrounds both electrodes. Tests have shown .thatthe, yielddn the region of the aforementioned maximum of the secondary emission with the, electrodes located. as in Fig. 3a isso much greater. than. when .positioned as in Fig. 311, that in the former case, the grid current will become negative asshown in. Fig. 1 whilst when in the position shown in Fig. 312' it always remains positive (Fig. 2) I If the other conditions that afiect tube operation remain unaltered, the electrode geometry, 1. e., the spacing and the relative position of the electrodes, is therefore of great importance; as

regards the shape of the grid-currentand rid voltage characteristic. This is due. to the field formation in the immediate vicinity of the grid surface which in the case of Fig, 3b is greatly influenced by the space charge surrounding the cathode. In this case not only does the larger field strength prevent the secondary electrons emerging mainly towards the axis from leaving the vicinity of the grid but the impact of the primary electrons which is mainly perpendicular is in itself the cause of a smaller yield. In the position shown in Fig. 3a less primary electrons reach the control grid but under much more favourable conditions for releasing and transmitting secondary electrons to the anode.

In another embodiment of the invention, as shown schematically in Figs. 4a and 4b, the cathode wires are evenly distributed around the electrode circumference. It will be readily appreciated-that in this case the effect of the rotation on the tube characteristic under consideration will be smaller, the maximum angle of rotation amounting to 15 in this particular case. According to the purpose for which the tubeis intended to be used it may be an advantage-for the cathode wires which are generally present in large numbers to be distributed evenly, 'or' in groups as shown in Figs. 3a and 3b,,whereby'in the latter event it is preferable if the number of groups corresponds to the number of grid rods. Transmitter tubes, particularly for small powers, are often constructed with spiral grids. In such cases the supporting rodsfor the grids'play the same part as the grid rods mentioned; above. In order to increase their influence when theyare rotated about the tube axis the ratio between the numberof cathode Wires and the. number of grid rods should be made'a whole number;- On the other hand when rod grids are used, thesensitiveness 'of the displacement can oftenbe increased when the ratio of the number of cathode wires to that of the grid rods is not a whole'number.

It is found that the'accuracy with which (the gridcurrent characteristic curves can be adjusted can, be. greatly, increased if the number of oath.- odewires is greater. than 'theinumber of. parallel grid'rods. 'B'oth'in "the case of an even orirregular distribution of the cathode wires around the periphery of the cylindrical array of cathode elements'itis an advantage if theseare'arr ranged in groups, whereby the wires-of'anyone group are subjected to a heating current of-the same'pola'rity. Between these wires and between these latter and the anode considerableforces prevail when the heating power and voltage is high. There is 'mutual repulsion .between' the wires of each groupand therefore thesemust'be connected together ina circumferential direction in "at, least one diametrical plane, the number of such planes depending upon the total lengthof the wires. In order to compensate the radial tensile pull of the anode these wires are also connected together by means of diametrical crosswires, diametrically opposed cathode'wires of. the same polarity being connected together. Inf-Fig. 4b such stiffening wires are indicated, T'bein'g the tangential and R the radial stifieners. These latter are 'expediently connected together at the uum will be readily understood with reference to Figs. 5-8. The demountable tube consists essentiallyzofan anode A insldeof which the cathode K and the grid G is located. The cathode K comprises two groups of parallel cathode wires K1 and K-z; that are connected attheir lower ends to. a disk or ring la, the. former group being fixed to the central rod E and the latter group K2 to the concentric tubular elements F. Elements E and F are held in position by cathode supporting disks J and U which are insulated from each by a cathode insulator L. The lower cathode disk U rests upon the annular disk M, the disks being detachably united and sealed to each other by thermoplastic material N to constitute a demountable joint that may be opened, upon heating of the sealing material, for removal of the cathode assembly. The control grid G is a spiral wire grid wound on grid supporting rods 0 which are fixed to a grid disk P that is spaced from the disk M by the insulating cylinder L. Between this latter flange P and the anode A is an anode insulator Q. Each group of cathode wires K1, K2 is provided with diametrical cross-wires or stifl'eners R1 (Fig. 7) and R2 (Fig. 8) respectively by means of which diametrically opposed wires of the same polarity are connected together, each group of stiffeners being located in a difierent diametrical plane. Circumferential stiffeners T1, T2 can also be provided. The envelope or wall of the tube is constituted by a number of sections namely, the disks J, N, U, M and P, the cylindrical insulators L, L' and Q, and the cylindrical anode A, the several adjacent wall sections being separable from and. sealed to each other, as is conventional in demountable tubes. The lower end of the anode A is connected, through the insulating end of the anode A is connected, through the insulating cylinder L", with the molecular vacuum pump S which establishes and maintains the desired degree of vacuum within the tube during operation thereof.

For adjustment of the operating characteristic of the tube by rotation of the cathode wires K1, K2 relatively to the grid or grid supporting rods 0 it is merely necessary to heat up the joint N between the disks M and U, say up to about 80 0., at which temperature it becomes plastic whereupon cathode disks U and J together with their respective cathode wires K2 and. K1 can then be rotated relatively to the grid supports 0. This rotational movement is thus achieved without breaking the tube joints or affecting the vacuum inside the tube.

The use of tubes according to the invention for push-pull connections is not only a great advantage as regards replacements but also as regards the possibility of rapidly compensating alterations in the performance of the tube, such as for instance when changes occur in the yield of the secondary emission due to vaporised cathode ma terial reaching the grid.

This application is a continuation-in-part of, and is substituted for, our copending application Ser. No. M1350, filed May 5, 1942, now abandoned.

We claim:

1. A demountable transmitting tube of the type comprising an envelope including a plurality of wall sections, a cathode and a control grid supported by wall sections insulated from each other, and a joint sealed by thermoplastic material be tween said supporting wall sections, characterized by the feature that the cathode consists of a plurality of parallel wires and the control grid consists of parallel rods, the cathode wires and 6 grid rodsbeing parallel to'and" both arranged around the common tube axis, said wall sections which support said cathode'and said control grid respectively being relatively rotatable for anglilar adjustment of the cathode wires and control grid rods upon softening of the thermoplastic sealing material while the tube is under vacuum.

2. Tube as in claim 1, wherein said axially parallel wires forming the cathode are nonuniformly spaced about the tube axis but mounted in groups.

3. Tube as in claim 1 wherein said cathode wires are non-uniformly spaced circumferentially in a number of groups equal to the number of axial rods of the grid.

4. Tube as in claim 1, wherein the control grid comprises a spiral winding on said rods the ratio of the number of cathode wires to the number of supporting rods is a whole number.

5. Tube as in. claim 1, wherein there is a whole number ratio between the number of cathode wires and grid rods, adjacent cathode wires of the same polarity being connected together in parallel in at least one diametrical plane in a circumferential direction and mutually stifiened by diametrical cross-connectors.

6. A demountable tube comprising a control grid electrode, cathode and anode electrodes, said cathode and grid electrodes each including a plurality of elements parallel to the axis of the demountable tube, a tube envelope including a plurality of wall elements of conductive and insulating material respectively, means supporting said cathode and grid electrodes upon conductive wall elements insulated from each other, and thermoplastic sealing material between said conductive wall elements which support said cathode and grid electrodes, respectively, the control grid elements and cathode elements being adjustable with respect to each other upon heating the joint to soften the sealing material.

7. A demountable tube as recited in claim 6, wherein said cathode electrode comprises a cylindrical assembly of parallel wires, said wires being non-uniformly spaced circumferentially in groups.

8. A demountable tube as recited in claim 6, wherein said cathode electrode comprises a cylindrical assembly of parallel wires, said wires being non-uniformly spaced circumferentially in groups, each group including a plurality of uniformly spaced wires.

9. A demountable tube as recited in claim 6, wherein said cathode electrode comprises a cylindrical assembly of parallel wires, said cathode wires being non-uniformly spaced circumferentially in groups, there being a group of cathode wires juxtaposed to each control grid rod.

10. A coaxial cathode-grid assembly for a vacuum tube, said assembly including a cathode comprising a cylindrical assembly of a plurality of parallel wires arranged in a plurality of groups of adjacent wires, there being an even number of more than three groups, a grid surrounding said cathode and including circumferentially spaced rods parallel to the cathode wires, the number of grid rods being equal to the number of groups of cathode wires, the cathode wires of each group being connected in parallel and the cathode wires of each group being connected in series with the cathode wires of another group.

11. A coaxial cathode-grid assembly as recited in claim 10, wherein circumferentially arranged REFERENCES CITED.

smimseemms Number Number The following meienences are :of record 1n1the file oitthiis patent Name Date f Stoek1e Sept:2B, -I920 No'lte *et a1; "Oct.--28=," 1 9-3U B01 "AugJ -1 8', 1931 lilifmiromtseffet a1; Jain; 5; 1932 Manthorne Huly'f25; 1 939 Carbonaura; Bec; 1 1 ,1940 Wing, Jr Jun'e ':80,='I942 Ronci Apr.2i),""1943 FOREIGN PATENTS I Country .4mate. Australia. De'c.-" 29 11939 Switzerland i -ilun'e -930;

Certificate of Correction Patent No. 2,443,237. June 15, 1948.

ARTHURZGAUDENZI ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 6, line 40, claim 6, after the word adjustable insert angularly; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 17th day of August, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

